Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$227.27	11.422%	$253.2288	$253.23	$253.25	$253.20
Purchase #2	$171.27	8.326%	$185.5299	$185.53	$185.55	$185.50
Purchase #3	$23.80	11.298%	$26.4889	$26.49	$26.50	$26.50
Purchase #4	$106.59	12.548%	$119.9649	$119.96	$119.95	$120.00
Purchase #5	$189.85	11.170%	$211.0562	$211.06	$211.05	$211.10
Purchase #6	$31.67	3.749%	$32.8573	$32.86	$32.85	$32.90
Purchase #7	$79.89	13.260%	$90.4834	$90.48	$90.50	$90.50
7 purchase totals =	$830.34		$919.6094	$919.61	$919.65	$919.70